This invention relates to a pattern reading system to be used for the recognition of characters and figures, and more particularly to a pattern reading system which, in the polygonal approximation of a given pattern such as characters and figures by the tracing of the contours of component characters and figures, enables such characters and figures to be approximated with polygons without bothering with minute convexities and concavities in their contours by allowing for tolerances in the calculation of inner products.
Differently from other characters, handwritten characters do not have fixed patterns and, therefore, are difficult to recognize. As a general measure for pattern recognition, there can be mentioned the feature extraction method which consists in providing a thinning operation and line approximation of patterns such as characters and figures or in effecting recognition of convexities and concavities in line segments of such patterns by extracting the geometric features of the character including the background (white region) by means of parallel processing. The former extraction method by use of axial line approximation of patterns suffers a disadvantage in that the characteristics of a pattern are confused due to the occurrence of unnecessary segments called "whiskers" which are involved in effecting the thinning operation for patterns and the disappearance of the delicate shapes of the patterns caused by the thinning operation and that the approximation of curves adds to the complexity of the representation of the curves.
The apparatus for accomplishing the extraction method for extracting the concave and convex segments of the given pattern by use of a two-dimensional parallel processor in accordance with a two-dimensional parallel processing is remarkably complicated and inevitably turns out to be expensive.
For the purpose of eliminating the disadvantages suffered by the conventional feature extraction methods, a group of studies including one by the present inventors resulted in the development of the systems disclosed in Japanese Patent Publications No. 1037/1982, and No. 23302/1982, (corresponding to U.S. Ser. No. 84,168, filed Oct. 12, 1979.)
These systems are based on one and the same operating principle that desired recognition of a given pattern is accomplished by tracing the contours of the pattern, determining a plurality of outermost points of the pattern in accordance with the distances from the starting point of tracing along the contours traced to these outermost points and the integrated values of the coordinates of these outermost points, dividing the contours into convex segments, concave segments, and hole segments in accordance with the data on the outermost points thereby quantizing the characteristics of the pattern and matching the quantized characteristics with entries in a dictionary prepared in advance.
The pattern reading principle described above provides global extraction of feature of the pattern without being affected by relatively minute local convexities and concavities in the contours. When the pattern happens to contain a convex structure within a concave structure, however, the systems of this principle are compelled to repeat the tracing of the portion of concave structure of the pattern. Since minute local convexities and concavities of the contours are recognized as such by relative decisions, there are times when these decisions will lack uniformity.